Project Summary The study of immune responses to HCV has provided important insight into protective immunity, but more research is needed to identify clear correlates of protective immunity for vaccine design. The overall goal of the proposed research project is to define the innate immune and T cell responses that allow protective immunity against the broadest array of infecting hepatitis C viruses by studying people who are repeatedly exposed to and control HCV. Longitudinal assessment of those who are repeatedly exposed with documented re-exposure to and control of multiple infections may represent the best opportunity to find correlates of truly protective immunity to mimic in vaccine development. A number of vaccine adjuvants activate innate immune sensing pathways that affect vaccine responses. Thus, we plan to assess the earliest innate response to HCV infection to identity those that play a key role in the priming, expansion, and polarization of effective adaptive immune responses and improve selection of a vaccine adjuvant that enhances induction of protective responses. We also plan to analyze T cell responses to HCV infection that result in control of HCV upon repeated exposure. Understanding protective T cell responses will enhance creation of a vaccine that induces T cells capable of clearing cells infected with any virus that evades the frontline neutralizing antibodies. We will analyze our T cell and cytokine data from this project in the context of antibody responses in the same subjects (Project 1- Ray) and with evaluation of the infecting HCV sequence (Project 3-Shaw). Combined data from this Project with Project 1 (Ray, humoral response to HCV) will allow us to determine how the innate response to HCV supports the generation of antibodies that effectively neutralize infection. Using sequence data from Project 3 (Shaw) in combination with data on T cell responses from this Project and neutralizing antibody responses in Project 1 will allow us to determine how repeated exposure to close but not identical viral sequence affects adaptive immune responses. An assessment of viral sequence homology and the effects on the downstream adaptive immune response will provide information relevant to several viral infections where viral sequence varies, including HCV, with the goal of increasing the chances that vaccination promotes adaptive immune responses that prevent rather than promote disease. In sum, we anticipate that the proposed research studying the innate and adaptive T cell immune responses of people who are repeatedly exposed but don't develop persistent HCV infection will define correlates of protective immunity to target in vaccine design.